1. Field of the Invention
The present invention relates to a high-pressure metal pipe with a connection head of a thick wall steel pipe with a relatively small diameter such as a high pressure fuel injection pipe having an outer diameter of the order of 4 mm to 20 mm and a wall thickness of the order of 1 mm to 8 mm frequently used for being arranged as a fuel supply piping in a diesel internal combustion engine. The present invention also relates to a method of forming the connection head and a connection washer for the connection head.
2. Description of the Prior Art
A conventional high-pressure metal pipe with a connection head of such a kind and a method of forming the head thereof are presented as an example shown in FIG. 1 and FIG. 2. In the example, an end portion of a thick wall steel pipe 11 is externally pressed in its axial direction by a punching die. This makes the end portion subjected to buckling to be press-formed into a flat-head-cone-like connection head 12 with the outer surface of the pipe 11 being provided as a seat surface 13 of the connection head 12. Outward expansion of the pipe wall in relation to the press forming with the buckling produces a deep and large annular sharp fold 15 or a pocket on the inner surface of the head. With such a state, thus constituted connection head is provided for being used at present. In addition, a washer 14 is fitted onto a lower neck portion of the connection head 12.
In such a conventional high pressure metal pipe with a connection head and a manufacturing method thereof, however, there was presented a problem in which the deep and large annular sharp fold 15 or a pocket produced on the inside the head becomes a possible start point of fatigue fracture due to repetitive high pressure imposed by high pressure fluid in the pipe when the pipe is arranged and used.
Moreover, as shown in FIG. 2, when a box nut 16 used in connecting the pipe to another one is excessively tightened without controlling tightening torque, the washer 14 was subjected to plastic deformation to be broken as shown in the figure. The tightening torque produces a force acting in an axial direction. At a top end portion of the washer 14, the force is divided into a component along the inclined seat surface 13 and a component vertically acting on the seat surface 13, of which a force resisting the tightening is a reaction against the component vertically acting the seat surface 13. Most of the reaction acts in a direction of the wall thickness of the pipe at the top end portion of the washer 14, by which the washer 14 is radially expanded in the diameter for being deformed to be broken. This causes a problem that makes the top end of the washer 14 bite into the inner surface of the box nut 16 to make it stick to the washer 14.
The present invention is made in view of the above problem in the prior art with an object of providing a high-pressure metal pipe with a connection head, a method of forming the connection head thereof and a connection washer for the connection head, in which, instead of the annular sharp fold or pocket, an annular groove can be formed on an inside face of the head as being shallow and having a gently sloping cross sectional outline form when forming the head to make it possible to eliminate fear of causing fatigue fracture inside the head and to prevent the nut from being stuck to the washer due to an excessive tightening torque.
In order to achieve the above object, the gist of the present invention is a high-pressure metal pipe with a connection head characterized by comprising a connection head provided at an connection end of a thick wall steel pipe with a relatively small diameter and a connection washer covering an outer surface of a lower neck portion of the connection head. The connection head has an outer face being provided as a flat-head-cone-like or flat-head-sphere-like seat surface for being fitted to a mating seat, and an inside face having a shallow and gently sloping annular groove produced as a result of deformation due to a press forming of the head. The connection washer has a step expanded diameter section at one end with a face perpendicular or inclined in cone-like to an axis of the washer, and a maximum diameter portion of the connection head is formed over the face of the one end with the step expanded diameter section, with a part of the connection head filling the step expanded diameter section.
Moreover, a method of forming a head of a high-pressure metal pipe is characterized by comprising the steps of providing a thick wall steel pipe with a relatively small diameter being cut for a specified length beforehand; providing a connection washer; preparing a chuck for holding the steel pipe together with the washer; preparing a punching machine having a die for forming the head of the high-pressure metal pipe; forming a step expanded diameter section at one end of the connection washer; fitting the connection washer near a connection end of the thick wall steel pipe onto outside thereof in coaxial so that the step expanded diameter section is on the connection end side; making the chuck hold the steel pipe together with the connection washer with a margin for forming the connection head being left on a top end side from the connection washer; and externally pressing the top end section of the steel pipe by the die of the punching machine in coaxial to form the connection head with the outer surface of the steel pipe being provided as a flat-head-cone-like or flat-head-sphere-like seat surface for being fitted to a mating seat so that the inside face of the connection head is formed to have a shallow and gently sloping annular groove, the connection washer covers an outer surface of a lower neck portion of the connection head, and a maximum diameter portion of the connection head is formed over the face of the one end of the washer with the step expanded diameter section with a part of the steel pipe filling the step expanded diameter section.
The method further comprises the step of forming the face of the one end of the connection washer with the step expanded diameter section as being perpendicular or inclined in cone-like to an axis of the washer.
In addition, the connection washer is characterized by providing at one end a step expanded diameter section covering an outer surface of a lower neck portion of the connection head of a high pressure metal pipe.
In the present invention, the step expanded diameter section is provided at one end of the washer covering an outer surface of the lower neck portion of the connection head. Thus, the step expanded diameter section functions to restrain outward expansion of the outer diameter of the molded portion for bringing the tube material to project toward inside to provide the shallow annular groove having a gently sloping cross sectional outline form instead of forming the annular groove as a sharp fold or pocket. Therefore, the possibility of the annular groove becoming a start point of fatigue fracture can be reduced which is due to stress concentration inside the head. Here, the connection washer refers to a washer or a sleeve washer.
Moreover, the structure, in which the maximum diameter portion of the connection head is over the face of the one end of the connection washer with the step expanded diameter section which face is formed as being perpendicular or inclined in cone-like to an axis of the washer, can prevent the nut from being stuck to the washer deformed to radially expand due to excessive tightening torque given to the nut. The structure provides the contact surface of the maximum diameter portion with the end face of the washer as also being perpendicular or inclined in cone-like to the axis. Thus, a reaction to a force, produced by the excessive tightening torque and acting on the contact surface in an axial direction, is made to act also in the axial direction or toward inside the washer. Therefore, no component acting in the direction of the wall thickness of the washer is generated to make it possible to restrain the radial expansion of the washer and to prevent the nut from causing a phenomenon of being stuck to the deformed washer.
In addition to the above working-effect, when the meeting face of the connection washer with the tightening nut is provided as a spherical face, an effect can be also obtained that can uniformly transmit the force acting in the axial direction onto the seat surface without losing the force even if there is a deviation between the axes of the washer and the nut.